This invention relates to films with thick or multiple layers of polymeric coating and processes for preparing such films.
Several methods are known for applying thick or multiple coating layers to films or other objects. For example, U.S. Pat. No. 3,959,526 discloses a process of preparing a high barrier, heat sealable packaging material having a low level of total retained solvents. A sub-coating of a high barrier vinylidene chloride copolymer and a top coating of a heat sealable vinylidene chloride copolymer are applied from solution to a film. Application of the top coating from a dilute solution containing about 5 to 10% solids to a solids coating weight of about 0.5 to 3 g/m.sup.2 provides a low level of solvent retained in the coatings after a drying step.
U.S. Pat. No. 4,781,978 discloses articles with a coating used for promoting adhesion. The coating is formed from a blend comprising at least one polymer containing carbonylamide functional groups (e.g. polyethyloxazoline) and at least one hydrophobic polymer substantially free of acidic functional groups. Coated articles such as PET film can be prepared by evaporating a solvent carrier of the polymer blend.
U.S. Pat. No. 3,950,579 discloses a method of forming relatively thick deposits of polymeric material on a surface of small threaded articles which comprises forming a thin coating on the surface of a solution of the polymeric material, preferably draining the excess solution, then drying the coating, applying a barrier coating such as polyvinyl alcohol to the polymeric material to protect it from attack by solvent, and applying a second thin coating of a solution of the polymeric material. Coating is by successive immersion in baths of the barrier material or by other bulk treatment. This treatment permits the required amount of polymeric material to be deposited in the grooves of the article while preventing articles in bulk from sticking together in an agglomerated mass. The polymeric material is a polyurethane or preferably an acrylic or methacrylic resin, and an adhesion promoting material such as a polyamide or a silicone resin is used. Such coatings provide increased friction between the threaded article and a mating nut.
Other references disclose film structures with varied polymer layers. U.S. Pat. No. 4,741,970 discloses a thermoplastic laminate structure wherein one of the layers is an adhesive comprising a poly-2-oxazoline. The adhesive is well suited for adhering saran to polypropylene.
U.S. Pat. No. 4,565,742 discloses a film laminate prepared by a variety of lamination and coating processes. The film comprises a base film of e.g. oriented polyester or nylon, a coating of polyvinylidene chloride, and a sealant layer of e.g. ethylene vinyl acetate copolymer. A second coating of PVDC can be applied to the base film by heat lamination or through an aqueous PVDC dispersion. When the base film is nylon, the first PVDC coating tends to prevent water in the second PVDC dispersion from wrinkling or curling the underlying film.
Japanese patent application 59-152929 discloses a method for treating a thermoplastic polyester container comprising coating the container with a polymer from dispersion or solution. In one example a first coating of saponified polyvinyl acetate is applied from solution, then a vinylidene chloride polymer latex, followed by drying.
The present invention provides a means for applying multiple layers of solvent-borne coatings to films without contamination of previously-applied layers by the solvent. The invention also provides films which have outstanding barrier and processing properties.